As used herein, the term “short circuit” refers to an abnormal connection of zero or relatively low impedance between live conductors having a difference in potential under normal operating conditions. A short circuit current is an over current, or more current than normal, which goes outside a normal current path when the current is shunted around a load.
Those of ordinary skill in the art know that a power supply is a device that provides electrical current to a load device. Many power supplies provide a direct current or “D.C.” In a motor vehicle, a power supply is frequently embodied as a battery capable of providing significantly more electric current than the electronic devices commonly found throughout a vehicle require. A mechanism for protecting a battery or other type of power supply device from short-circuits is thus important to both the vehicle and various devices that are provided power.
Prior art short-circuit protective devices for electronic circuitry and devices typically use a small-valued resistance through which all of the current to an electronic load device is provided. The amount of current provided to such a load is determined by measuring the voltage drop across the small-valued resistance and, using Ohm's Law, calculating the current through the resistance. Those of ordinary skill in the art know that such a determination is made by dividing the voltage drop across the resistance by the value of the resistance itself.
Problems with prior art short-circuit protection devices that require a current-sensing resistor include the cost of a precision resistance, and a device to measure the voltage drop and cut off current when the voltage drop exceeds some pre-determined value. A more direct, simpler and less expensive method and apparatus for providing short-circuit protection to power supply devices would be an improvement over the prior art.